Always redirect the actor to an offscreen buffer even if it is fully opaque.
Only redirect
the actor if it is semi-transparent and its has_overlaps()
virtual returns true.
Only redirect the actor if it is the most efficient thing to do based on its recent repaint behaviour. That means when its contents are changing less frequently than it's being used on stage.
Possible flags to pass to
clutter_actor_set_offscreen_redirect().